Catalysts for aldol condensations

ABSTRACT

Heat treated anionic clay mineral is an improved catalyst for the conversion of acetone to mesityl oxide and isophorone as well as for the aldo condensation of other carbonyl-containing compounds.

This is a division of Ser. No. 384,212 filed June 2, 1982.

BACKGROUND OF THE INVENTION

This invention pertains to aldol condensations catalyzed by heat-treatedsynthetic anionic clay minerals and more particularly to the use ofthese catalysts for the conversion of acetone to mesityl oxide andisophorone.

The aldol condensation of active hydrogen-containing organic carbonylcompounds has found wide use in the chemical industry for the synthesisof a myriad of organic compounds. The earliest catalysts used for thiscondensation reaction were bases, such as, alkali metal hydroxides whichhave been used for the production of 2-ethylhexanediol-1, 3,2-ethylhexanol-1, diacetone alcohol, isophorone, mesityl oxide,methylisoamyl ketone, methylisobutyl ketone and the like.

A variety of methods has been disclosed in the literature forconverting, for example, acetone by aldol condensation into a widespectrum of products particularly isophorone and mesityl oxide which areused in industrial solvents and as chemical intermediates for resins,dyes, intersecticides, and the like. By-products which arise from thegeneral aldol condensation reaction wih acetone include diacetonealcohol, 4,4-dimethyl-hepta-2,6-dione,4,6-dimethyl-hepta-3,5-diene-2-one, 3,5,5-trimethyl cyclohex-3-ene-one,mesitylene, 2,2,6,6-tetramethyl tetrahydropyran-4-one, xylitones, andisoxylitones, as well as various unidentified high boilers and tars. Thespecificity of the reaction must be controlled for commercial success inorder to direct conversion of acetone to the desired end products.

Examples of prior catalysts used for conversion acetone to isophoroneand mesityl oxide are: alkali metal hydroxides, such as, sodium,potassium, and lithium hydroxide; alkaline earth hydroxides, such ascalcium, magnesium, strontium and barium hydroxide; calcium aluminate,calcium borate, potassium zincate, magnesium plumbate, barium aluminate,lithium plumbate, sodium borate, strontium stannate, potassium stannate,calcium borate, magnesium antimonate, sodium antimonate, calciumarsenate, sodium arsenate, potassium titanate, calcium zincate,magnesium aluminate, beryllium aluminate, cesium borate, rubidiumarsonate, lithium phosphate, magnesium oxide, and the like.

In addition a recently discovered magnesium-aluminum hydroxide basedcatalyst has been described in U.S. Pat. No. 4,165,339 which affordsefficiencies of about 80 percent (acetone to mesityl oxide andisophorone) at a conversion of about 15 to 18 percent per pass.

It is an object of this invention to provide an aldol condensationcatalyst particularly for the conversion of acetone to mesityl oxide andisophorone having both enhanced efficiencies and conversions of acetone.

It is a further object of this invention to control the condensation ofacetone to produce chiefly mesityl oxide and isophorone and in additionto limit the molar ratio of mesityl oxide: isophorone produced to a lowvalue, preferably less than one, to conform to tne commercial demand forthese two products.

It is still a further object of this invention to provide a catalyst forthis aldol condensation of acetone having the following properties:

High and constant activity

Reproducible activity

Long catalyst life

Ability to be regenerated readily

Consistent in selective production of

mainly mesityl oxide and isophorone

Cheaper and available

It is also an object of this invention to provide a catalyst and methodfor the aldol condensation of active hydrogen-containing organiccarbonyl compounds in general.

SUMMARY OF THE INVENTION

An improved catalyst for aldol condensations of active hydrogencontaining organic compounds has been developed. These materials arebased on synthetic anionic clay minerals, which after appropriate heatactivation, result in these superior catalysts.

These synthetic inorganic materials belong to thehydrotalcite-sjogrenite-pyroaurite and related mineral classes. Theirideal composition is represented by the generic formula:

    M.sub.m N.sub.n (OH).sub.2m+2n A.sub.a.bH.sub.2 O

wherein

M is a divalent metal cation;

N is a trivalent metal cation;

A is a mono-, di- or trivalent anion which decomposes at about 300°-500°C. to hydroxyl ions;

m and n are integers such that m/n has values of 1 to about 6;

a is an integer with the provisos that when A is a monovalent anion a=n,when A is a divalent anion a=1/2n, and when A is a trivalent aniona=1/3n; and

b is an integer having values of 0 to 10.

These synthetic anionic clay minerals are converted to the actualcatalysts for aldol condensations by heating them to a temperature ofabout 300° C. to about 600° C. whereby the anion moiety is decomposed tohydroxyl ion.

The structure of these materials is essentially that of brucite(Mg(OH)₂). In brucite the metal is in an octahedral environment ofhydroxyls. These octahedra share edges and thereby form extended sheets.These sheets are stacked on top of each other much like sheets of paper.In the hydrotalcite, for example, the magnesium and aluminum are inthese octahedra which generate the metal oxide sheets. Since eachaluminum cation has one more positive charge than the magnesium cation,the sheets have gained one unit of positive change per aluminum ion.This is compensated for by suitable anions located interstitially.Additionally, there are some water molecules located between each metalion sheet. These minerals can be prepared synthetically and this allowsa variation of the M⁺² /N⁺³ ratio, a wide variation of the kind of anionas well as various other features which will be discussed below.

Heat treatment of these synthetic materials, which by themselves areonly partly active, converts them into highly active catalysts. Onheating to over 300° the interstitial water molecules and thedecomposition product(s) of the anion are expelled and hydroxyl groupsare converted to metal oxide and water. For hydrotalcite thestoichiometry is as follows:

    Mg.sub.6 Al.sub.2 (OH).sub.16 (CO.sub.3.sup.=).4H.sub.2 O→Mg.sub.6 Al.sub.2 O.sub.7 (OH).sub.2 +CO.sub.2 +12H.sub.2 O

The volatile carbon dioxide and water escape and the residue is a veryintimate mixture of metal oxides with approximately one hydroxide perM⁺³ remaining on the oxide skeleton. Further consequences of thisheating process are discussed below.

The general method for the preparation of the catalyst is illustrated bythe preparation of Mg/Al/carbonate hydrotalcite which involves theaddition of mixed magnesium/aluminum nitrates, sulphates or chlorides asan aqueous solution to a solution of a stoichiometric amount of sodiumhydroxide and carbonate at about 25-35° C. with vigorous stirring overabout a several-hour period producing a slurry. This slurry is thenheated for about 18 hours at about 50°-200° C. (preferably 60°-75° C.)in order to allow a limited amount of crystallization to take place.After filtering the solids, and thorough washing and drying, the drysolids are recovered.

This procedure is readily adaptable to variations in the Mg/Al ratio,the anions, and cation substitution. The presence of the sodiumcarbonate materially enhances the rate of filtration; the absence ofsodium carbonate results in a mud which is very difficult to filter.

The rate of metal ion aodition to the aqueous caustic/carbonate solutionis not very critical nor is the reaction temperature. The rate ofaddition can be varied widely. The important feature is an adequatemixing of the metal ion solution and the caustic-carbonate solution. Inthe absence of efficient agitation, undesired reactions occur which donot lead to a useful product. The addition temperature is best kept atbelow 100° C.

This results in a slurry of magnesium-aluminum hydroxide which isessentially amorphous to X-rays. Only after a suitable heat aging orcrystallization do these filtered and dried solids have a well definedX-ray powder pattern. This crystallization process is an important partof this catalyst preparation. When the crystallization temperature istoo low (less than 50°), the rate of crystal formation is so slow as tobe impractical. At elevated temperatures the crystal growth is veryrapid and may yield too large a crystal (greater than 200°/18 hr). It isbest to choose an intermediate temperature of about 65°-75°/18 hr. Thisyields a crystal of about 150-300 A in size which has a surface area of100-120 m² /g (BET/N₂ technique).

The subsequent heat treatment is very important. This may be carried outbetween 300° and 500° C. in air or an inert gas stream or even undervacuum. The heating temperature is very critical. At or below 300° C.the hydrotalcite decomposition process is slow and incomplete. Above600° C. the resulting metal oxide mixture begins to sinter and losesurface area, pore volume, as well as form a catalytically inactivephase (spinel-MgAl₂ O₄). The temperature range of 400°-450° C. appearsto maximize the catalyst's surface area and the pore volume and drivesthe reaction to completion in a reasonable period of time (18 hrs).

At this point the fine powder can be pelleted or extruded to formparticles which are wear and impact resistant and can functioneffectively in fixed-bed catalytic converters. Usually some graphite(less than 2%) is added to aid the forming process.

In order for this heat-treated material to be an active and effectivecatalyst, it is necessary that the interstitial anion conforms tocertain criteria. On heating to 350°500° C. the anion must:

Decompose to form a volatile gas leaving behind a hydroxyl group:

    H.sub.2 O+(CO.sub.3.sup.=)→2OH.sup.- +CO.sub.2

    H.sub.2 O+2NO.sub.3.sup.- →2OH.sup.- +2NO.sub.2 +0.5O.sub.2

Decompose to form an inert metal oxide and a hydroxyl group:

    H.sub.2 O+Cr.sub.2 O.sub.7.sup.= →Cr.sub.2 O.sub.3 +1.5O.sub.2 +2OH.sup.-

In the event that the interstitial anion cannot decompose in this mannerat less than 500° C., then the resulting heated material will besubstantially inactive as a catalyst. The reason for this is that theanions remain intact and cannot generate the catalytically neededhydroxyl group. Thus SO₄ ⁼, PO₄ ⁼, ClO₄ ⁻, BO₃ ⁼, F⁻, Cl⁻, Br⁻, and I⁻do not decompose or volatilize under these circumstances, hence theheated material lacks catalyst activity.

Particularly desirable interstitial anions appear to be the long chainaliphatic alpha-omega dicarboxylates such as adipic, decane, anddodecane dicarboxylates. These appear to function in a dual manner:

These large anions expand the space between the metal hydroxide sheetsfrom about 3-5 Å to about 20 Å.

On oxidative burn-off, the volume of hydrocarbon to be burned to CO₂ andH₂ O is such that it expands the lattice even more, thereby resulting incatalysts which have unusually high surface areas (about 250 m² /g) andpore volumes (about 1 cc/g).

This results in very active catalytic materials.

While acetone is the preferred active hydrogen containing organiccarbonyl substrate used with these hydrotalcite catalysts, because ofthe commercial importance of its aldol condensation products, i.e.,isophorone and mesityl oxide, other substrates readily undergo aldolcondensation over these catalysts. Other exemplary substrates arepresented below.

The preferred temperature for converting acetone to mesityl oxide andisophorone using the catalysts of this invention lies in the range ofabout 250° to about 350° C. with a more preferred range lying in therange of about 280° to about 320° C.

Pressure is not narrowly critical but pressures of about 1 to about 5atmospheres are preferred. If desired the conversion of acetone with thecatalysts of this invention can be effected at atmospheric and below aswell as higher atmospheric pressures.

The feed rate of acetone is not narrowly critical but it is preferredfor efficient operations to range between about 20 and 140 pounds ofacetone per/hour/foot³ of catalyst. This corresponds to an hourly vaporspace velocity of about 90 to about 700 cubic feet of gaseous acetoneper cubic foot of catalyst per hour. At about 300° C. and 3 atmospheres,the preferred contact time is about 5 to about 40 seconds.

It is preferred to hold percent conversion of acetone in the range ofabout 7 to about 40 percent by weight.

The life of the catalysts of this invention is surprisingly long and isin excess of about 25,000 hours for the efficient conversion of acetone.An unexpected attribute of these catalysts is the fact that their lifecan be extended further by regeneration consisting of heating thecatalyst in the presence of air or oxygen at a temperature in the rangeof about 250° C. to 450° C. thereby burning off any adhering polymer andnon-volatile by-products. Surprisingly the regenerated catalyst is asactive and efficient and in many cases more active and efficient thanthe original catalyst.

The terms conversion and efficiency of the acetone conversion are usedin this invention as defined below:

    Conversion=10.sup.2 ×(B/A)

    Efficiency=10.sup.2 ×(MSO+I)/B

Where:

A=Total Acetone equivalents fed

B=Total Acetone equivalents in product(s)

MSO=Total equivalents of acetone in the mesityl oxide product

I=Total equivalents of acetone in isophorone product.

The term "Acetone Equivalent" is one for acetone, two for mesityl oxideand three for isophorone for purposes of this disclosure. It simplyaccounts for each mole of acetone fed passing through to the reactorwhether in reacted or unreacted form.

While the highest rates and efficiencies are obtained by using ananhydrous acetone feed having a purity of 99 percent or greater, thisinvention can be used with acetone having a purity as low as about 70percent by weight with the balance being mesityl oxide, water and othermaterials, such as, isopropanol, hexenes, and the like.

The conversion of acetone to mesityl oxide and isophorone according tothis invention is preferably carried out over a fixed catalyst bed.

The catalysts of this invention do not require a support. They can bepelleted, extruded or shaped into any desired form. However, if desiredthey can also be formulated to be carried on an inert material.

The testing of these catalyst compositions was carried out by twomethods. The first involved the use of a pulse reactor-gaschromatographic combination which yields rapid and semi-quantitativedata. This was used principally as a screening tool to detect highlyactive catalysts for subsequent testing. Also the reaction chemistry andother features were examined by this technique. The second method was aone-inch i.d. pilot plant reactor. In this latter device, long-termtesting was carried out.

The initial screening operations used in the discovery of this catalystsystem were effected by means of a pulse reactor consisting of amodified Hewlett-Packard Model 5750-B gas chromatograph. The gaschromatograph separation column was 10 feet long and 1/8" in diameterpacked with 20 percent Carbowax 20 M (Trademark of Union CarbideCorporation for polyethylene glycol having a formula molecular weightrange of about 18,000) on Chromosorb T (a polytetrafluorethylene supportsold by Johns-Manville Co.)

The programming schedule was 70° to 210° C. at 8°/min. Detection was byfid (flame ionization detection) although the less sensitive to (thermalconductivity) mode can also be used. The detector temperature was 300°C. Peak integration was carried out electronically.

The injection port kept at 300° C. was 1/4 inch i.d. into which a 2 mmo.d. glass liner filled with catalyst (about 0.05 g.) was inserted.Specially cut silicone rubber septa prevented gases from by-passing thisglass catalyst holder.

In the general procedure six 25 microliter fractions of acetone wereinitially injected into the catalyst bed. These injections were carriedout in rapid succession; after this the catalyst and the separationcolumn was cleared of all reaction products by sweeping helium throughfor about 2 hours. After these 2 microliter injections of acetone wereused to measure the initial catalyst activity.

The pilot plant reactor is described below:

ONE-INCH PILOT PLANT REACTOR

This device consists of a 1" i.d. pipe (300 cm long) made of 304stainless steel. The bottom 165 cm contained about 1 liter of catalyst.A 1/4" thermocouple well went through the center of this catalyst bed.In it were 6 thermocouples, equally spaced. Readings were on amultipoint recorder. On each end of the catalyst bed was a glass woolplug (7 cm) and a Carpenter "Neva-Clog" screen. Before the catalyst bedwas a 120 cm preheat section of 1/4" glass balls. Liquid acetone waspumped with a reciprocating plunger pump into a tubular heat exchanger(2 ft.² surface area, steam heated 190 psi) and then directly onto theglass bead section. Vapor flow was in a downward direction. Heating wasby 3/4"-high temperature glass fiber insulated tapes which werecontrolled by temperature controllers. The reactor pressure wascontrolled with appropriate valves. Following this was a 2 ft² heatexchanger. Weights (in and out) were on 100 kg. balances (±25 g.).Usually the material balance was within 2%. Gas formation - invariablynil-could be checked with a wet test meter.

Data from this pilot plant reactor can be quantitatively related toplant scale operations.

ANALYTICAL METHODS

Water was determined by Karl Fischer titration or by using thermalconductivity detection. The reactor crudes were analyzed by gaschromatography. Area-wt. % correlations were established using syntheticknown samples.

Typical pulse-reactor results are presented later. They were calculatedfrom the pulse reactor-gas chromatographic runs carried out by the aboveprocedure. Calcium hydroxide, a commonly used heterogeneous catalyst foracetone aldol condensations, was added as a reference but was relativelyinactive.

The activity of each catalyst can be inferred from the recovered acetonepercentage. The smaller this number the more acetone is converted, themore active the catalyst is.

The term "active hydrogen-containing organic compounds" as used hereinincludes those having the group ##STR1## adjacent to a aldehydic orketonic carbohyl group, a nitro group, a cyano group and other electronwithdrawing groups such as those present in quaternary salts.

Preferred active hydrogen containing organic carbonyl compounds whichare susceptible to aldol condensation using the catalysts of thisinvention include aliphatic aldenydes, such as, formaldehyde inconjunction with other active hydrogen containing compounds,acetaldehyde, n-butyraldehyde and the like; aliphatic ketones such asmethyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, and thelike; cycloaliphatic ketones, such as, cyclohexanone, as well asacetone.

The above described catalysts unexpectedly demonstrate selectivereactivity even for such closely related aliphatic aldehydes asn-butyraldehyde and its isomer isobutyraldehyde. It was demonstratedthat n-butyraldehyde reacted over 8 times faster than isobutyraldehydein an aldol condensation using these catalysts.

The invention is further described in the examples which follow. Allparts and percentages are by weight unless otnerwise specified.

EXAMPLE 1 Preparation of Mg-Al-CO₃ Hydrotalcite Catalyst

A 5-liter, 4-necked round bottomed flask was equipped with an additionfunnel, mechanical stirrer, reflux condenser, and thermometer. It wasnitrogen purged and a solution of 480 g 50% aqueous NaOH (6.0 mole) and100 g NaCO₃ was added to 2000 ml distilled water. To this was added asolution of 384 g Mg(NO₃)₂.6H₂ O(1.50 mole) and Al₂ (NO₃)₃.9H₂ O(1.00mole) in 1600 ml distilled water over a 2-hour period with goodmechnical agitation. There was a slight exotherm and a white, milky ppt.appeared at once. At the end the slurry was not very thick. Thetemperature was then adjusted to 65° C. and kept there for 18 hours.After cooling the slurry was filtered, the solid washed twice withdistilled water, and dried 125° C./vac/18 hours. This results in about170 g of a white hard solid. The X-ray powder patterns showed a verywell developed hydrotalcite pattern (ASTM D-22-700). The peaks arerelatively broad which can be attributed to the small crystal size(about 150 A). A typical analysis is shown below:

    ______________________________________                                        Component        Found (Wt. %)                                                ______________________________________                                        Ash              57.39                                                        Mg (on ashed sample)                                                                           35.34                                                        Al (on ashed sample)                                                                           17.72                                                        Na               0.0058                                                       N                0.012                                                        C                2.50                                                         Mg/Al ratio      2.24                                                         ______________________________________                                    

Heat treatment was carried out in a muffle furnace at 450° C. in air for18 hours.

EXAMPLES 2-7

In order to demonstrate the use of the calcined synthetic hydrotalciteof this invention as a catalyst not only for the condensation of acetonebut as a general aldol condensation catalyst, the following compoundswere also used as substrates in place of acetone: methylisobutylketone,cyclohexanone, acetaldehyde, a mixture of acetaldehyde and benzaldehyde,and butyraldehyde.

The pulse reactor described above was employed for those experiments at300° C. using 0.050 g of 50/80 mesh, heat activated synthetichydrotalcite catalyst prepared as described above. The catalyst had aMg/Al ratio of approximately 2.6 and a BET[S. Brunauer, P. H. Emmett andE. Teller, J. Amer. Chem. Soc., 60, 309 (1938)]surface area of 155meters² /g. The catalyst was further activated with 150 microliters ofacetone (300° C. and 60 psig of helium). In each run 2 microliters ofthe substrate was injected into the pulse reactor. The products wereanalyzed by gas phase chromatography using the area % of each product asan indication of the relative yields of products of each run.

As a standard for comparison, acetone was run first, the effluent fromthe reactor contained 45% acetone, 2.1% mesityl oxide oxide 2% unknownmid-range products, 36.2% isophorone, 7.5% isoxylitones and 6.6%tetralone.

Methylisobutylketone yielded 73.3% methyisobutyl-ketone, 16.5%diisobutyl ketone and unknown mid-range products of 4.3% and 1.3% andhigh boilers of 2.7% and 1.1%.

Cyclohexanone produced an effluent containing 58.5% cyclohexanone, 1.8%and 1.6% of mid-range unknowns, 23.9% and 12.9% respectively of productshaving the structures ##STR2## Acetaldehyde afforded an effluentcontaining 19.7% acetaldehyde, 21.4% of dialdehydes, 34.1% of C₆aldehydes and unknowns of 2.1%, 4.0%, 2.7%, 6.8% and 1.4%.

A mixture of acetaldehyde (0.5 ml) and benzaldehyde (1.5 ml) yielded aneffluent containing 0.7% acetaldehyde, 89.4% benzaldehyde, 3.8% ofunknowns and 3.3% of an aldehyde having the structure ##STR3##

Butyraldehyde yielded an effluent containing 47.2% unreactedbutyraldehyde, 36.6% C₈ aldehyde and the remainder were six unknownfractions.

EXAMPLES 8-12 a-d

Several compounds have been prepared in which substitutions of ions havebeen made in the hydrotalcite structure:

    (M.sup.+2).sub.6 (M.sup.+3).sub.2 (OH).sub.16 (X.sup.-).sub.2.4H.sub.2 O

wherein M⁺² is Mg⁺⁺, M⁺³ is Al⁺³ and (X⁻) is CO₃ in the synthetichydrotalcite catalyst of this invention. However, this invention alsocovers hydrotalcite related structures where M⁺² is Zn, Ni, Co, Cr, orNi/Mg mixtures in place of Mg. These were tested for catalytic activityin the condensation of acetone. The results are shown in Table 1compared with the original hydrotalcite containing Mg.

These data demonstrate that an isomorphous replacement of the divalentcation in the hydrotalcite lattice does not materially affect tnecatalytic effect of the resultant catalyst for the aldol condensation ofacetone.

EXAMPLE 13-15

Similarly the replacement of Al⁺³ in the original hydrotalcite by Fe⁺³and Cr⁺³ yielded hydrotalcites which were catalytically active for thealdol condensation of acetone. As shown in Table 2, the activity of theFe⁺³ containing catalyst was virtually identical to that of the Al⁺³isomorph. The Cr⁺³ containing catalyst became highly active only on heattreatment at 400° C. The replacement of Al⁺³ by a mixture of Al⁺³ andCr⁺³ also afforded active aldol condensation catalysts.

                                      TABLE 1                                     __________________________________________________________________________    EFFECT OF ISOMORPHOUS SUBSTITUTION OF M.sup.+2 IN THE                         HYDROTALCITE LATTICE ON CATALYTIC ACTIVITY                                               Example.sup.a                                                                 8  9  10 11 12a                                                                              12b  12c  12d                                       __________________________________________________________________________    M.sup.+2   Mg Zn Zn Ni Co Ni + Mg                                                                            Mg   Zu                                        M.sup.+3   Al Al Al Al Al Al   Al + Cr                                                                            Cr                                        M.sup.+2 /M.sup.+3                                                            Charged    2.00                                                                             2.00                                                                             2.00                                                                             2.00                                                                             2.00                                                                             3.00 3.00 3.00                                      Product Analysis                                                                         2.24                                                                             2.66                                                                             2.66                                                                             2.07                                                                             2.16                                                                             2.87 2.45 3.03                                      X-ray.sup.b                                                                              HT HT HT HT.sup.c                                                                         HT.sup.c                                                                         HT   HT   HT                                        Carbon Theory (%)                                                                        1.81                                                                             1.32                                                                             1.32                                                                             1.38                                                                             1.38                                                                             1.70 --   1.33                                      Carbon Found (%)                                                                         2.50                                                                             1.32                                                                             1.54                                                                             1.71                                                                             1.78                                                                             2.22 2.21 2.45                                      Pulse Reactor                                                                 Catalytic Activity                                                            Acetone Conv. (%)                                                                        24.6                                                                             12.5                                                                             10.5                                                                             34 22.8                                                                             37   30   11.1                                      Conv. Eff. (%)                                                                           76.3                                                                             86 94 66 91.4                                                                             --   --   99.7                                      __________________________________________________________________________     .sup.a All preparations were carried out as per Example 1 except Example      10. In this preparation the metal nitrate and causticcarbonate solutions      were added at equal rates to a wellstirred reactor. Subsequent treatments     were unchanged.                                                               .sup.b HT--hydrotalcite.                                                      .sup.c Strong fluorescence.                                              

                  TABLE 2                                                         ______________________________________                                        EFFECT OF ISOMORPHOUS SUBSTITUTION OF                                         M.sup.+3 IN THE HYDROTALCITE LATTICE                                                       Example.sup.a                                                                 13       14     15                                               ______________________________________                                        M.sup.+3       Al         Cr     Fe                                           M.sup.+2       Mg         Mg     Mg                                           M.sup.+2 /M.sup.+3                                                            Charged        2.00       2.00   2.00                                         Product Analysis                                                                             2.24       1.88   2.11                                         X-ray.sup.b    HT         HT.sup.c                                                                             HT.sup.c                                     Carbon Theory (%)                                                                            1.81       1.62   1.60                                         Carbon Found (%)                                                                             2.50       1.64   1.72                                         Pulse Reactor                                                                 Catalytic Activity                                                            Acetone Conv. (%)                                                                            24.6       23.2   26.5                                         Conv. Eff. (%) 76.3       86.0   80.5                                         ______________________________________                                         .sup.a Preparations were carried out as per Example 1.                        .sup.b HT = hydrotalcite.                                                     .sup.c Strong Fluoresence.                                               

EXAMPLES 16-21

The data in Table 3 illustrate that hydrotalcites can be synthesized inwhich the Mg/Al ratio varies between 1.38 and 6.27.

                  TABLE 3                                                         ______________________________________                                        EFFECT OF VARIATION OF HYDROTALCITE                                           Mg/AL RATIO ON CATALYTIC ACTIVITY                                                        Example.sup.a                                                                 16   17      18     19    20   21                                  ______________________________________                                        Mg.sup.+2 /Al.sup.+3                                                          Charged      1.00   1.33    2.00 2.50  3.03 5.0                               Product      1.39   NA      2.24 2.27  3.04 6.27                              X-ray.sup.b  HT.sup.+                                                                             HT      HT   HT.sup.d                                                                            HT.sup.e                                                                           HT.sup.d                          Carbon Theory (%)                                                                          --     --      1.81 1.81  1.99 --                                Carbon Found (%)                                                                           2.22   NA      2.50 2.25  2.36 1.42                              Pulse Reactor                                                                 Catalytic Activity                                                            Acetone Conv. (%)                                                                          37.5   21.0    24.6 15.0  22.5 24.2                              Conv. Eff. (%)                                                                             83.8   85.6    76.3 88.9  81.0 91.1                              ______________________________________                                         .sup.a Preparations were carried out as per Example 1 except that the         Mg--Al ratios were varied.                                                    .sup.b HT = hydrotalcite.                                                     .sup.c Includes a trace of hydromagnesite Mg.sub.2 (OH).sub.2 (OH).sub.2      CO.sub.3.                                                                     .sup.d Plus Al(OH).sub.3 Bayerite, Gibsite, and Norstrandite.            

                                      TABLE 4                                     __________________________________________________________________________    EFFECT OF ISOMORPHOUS REPLACEMENT OF INTERSTITIAL ANIONS                                           Example.sup.a                                                      22       23   24  25  26   27  28   29   30     31                  __________________________________________________________________________    Preparative                                                                             Metal SO.sub.4.sup.═                                                               Metal                                                                              Metal                                                                             Metal                                                                             Metal                                                                              Metal                                                                             Metal                                                                              Metal                                                                              Metal  Metal               Conditions                                                                              w/o CO.sub.3.sup.═                                                                 SO.sub.4.sup.═                                                                 Cl.sup.-                                                                          Cl.sup.-  w                                                                       NO.sub.3.sup.-                                                                     NO.sub.3.sup.-                                                                    NO.sub.3.sup.-                                                                     NO.sub.3.sup.-  w                                                                  NO.sub.3.sup.-                                                                       NO.sub.3.sup.-                                                                w                                      w CO.sub.3.sup.═                                                               w/o CO.sub.3.sup.═                                                                w/o  w/o w NO.sub.3.sup.-                                                                   OAc.sup.-                                                                          n-C.sub.4 H.sub.9                                                             CO.sub.2.sup.-                                                                       oxalate                                     CO.sub.3.sup.═                                                                    CO.sub.3.sup.═                                                                 CO.sub.3.sup.═                                                                excess                               Filtration                                                                              poor     good very                                                                              good                                                                              very good                                                                              poor poor fair   fair                Characteristics                                                                         weak Ht  HT   poor                                                                              HT  poor HT  HT   HT   diffuse                                                                              HT                  X-ray.sup.b                                                                             "MgAlOHSO.sub.4".sup.c                                                                      HT      HT                                            Mg/Al Charged                                                                           1.88     1.88 2.00                                                                              2.00                                                                              2.00 2.00                                                                              3.33 2.00 2.00   2.00                Mg/Al Product                                                                           2.50     2.05 2.32                                                                              2.01                                                                              2.56 2.24                                                                              3.50 2.57 1.97   2.92                Analyses (%)                                                                  S         4.73      .00 --  --  --   --  --   --   --     --                  Cl        --       --   5.38                                                                               .00                                                                              --   --  --   --   --     --                  N         --       --   --  --   .77  .12                                                                              2.01 1.47 1.60    .04                C          .63     2.40 1.22                                                                              2.41                                                                               .88 2.50                                                                               .59 0.58 13.45  4.34                Pulse Reactor                                                                 Catalytic Activity                                                            Acetone Conv. (%)                                                                       0        26   10.3                                                                              35.6                                                                              19.8 24.6                                                                              17.9 24.7 44.3   32.0                Conv. Eff. (%)                                                                          --       78   91.9                                                                              85.6                                                                              85.5 76.3                                                                              80.5 84.7 84.1   86.0                __________________________________________________________________________     .sup.a Preparations were carried out as per Example 1 except for              appropriate substitutions as indicated.                                       .sup.b HT--hydrotalcite.                                                      .sup.c Presence of Mg--Al hydroxy sulfates.                                   .sup.d w = with.                                                              .sup.e w/o = without.                                                    

EXAMPLES 22-31

The interstitial anion or anions are an essential part of thehydrotalcite lattice. In nature normally only the carbonate is found.Synthetic hydrotalcites can be made which contain many other anions inthe crystal lattice. However, the standard procedure of Example 1 couldnot be used when sulfate was substituted for carbonate because theresultant precipitates were thin and difficult to filter and did notcrystallize into the hydrotalcite lattice on heating at 65° C.

Table 4 shows the effect of isomorphous replacement of interstitialanions in the hydrotalcite lattice. Divalent anions from dibasic acidshaving 1 to 12 carbons can be used.

EXAMPLE 32

An evaluation of the MgO-Al-CO₃ catalysts (heat treated hydrotalcite)prepared as in Example 1 was carried out in the 1 inch Pilot PlantReactor described supra using acetone as the substrate 23%. Conversionand 77% efficiency to isophorone and mesityl oxide and other pertinentdata are presented in Table 5.

The synthetic hydrotalcites of this invention freshly heat-activated(450° C. in air for 18 hours) show ion exchange activity as inorganicanion exchangers. Above 50 percent exchange or adsorption of fluorideand such multivalent anions as sulfate, sulfite, sulfide, carbonate,phosphate, chromate, oxalate, and acetate took place with thishydrotalcite.

                  TABLE 5                                                         ______________________________________                                        EVALUATION OF HYDROTALCITE IN 1" REACTOR .sup.1                               ______________________________________                                        Catalyst             Hydrotalcite 1/4"                                                             Tablets                                                                       (Heated 400°)                                     Run No.              32                                                       Results                                                                       Acetone Conversion (%)                                                                             23.3                                                     Efficiency to MSO + 1                                                                              77.7                                                     MSO/I (wt.)          0.32                                                     Crude Analyses (dry basis, wt. %)                                             Acetone              80.7                                                     Mesityl Oxide        3.70                                                     Isophorone           11.6                                                     Midrange unknown products                                                                          0.66                                                     Isoxylitones         0.82                                                     Tetralone            2.50                                                     Conditions                                                                    Feed Rate (g/hr)     680                                                      Temperature (°)                                                                             300                                                      Pressure (psi)       40                                                       Time on Stream (hr)  450                                                      ______________________________________                                         .sup.1 Catalyst bed depth 80".                                           

Although the invention has been described in its preferred forms with acertain amount of particularity, it will be understood by those skilledin the art that the present disclosure has been made only by way ofexample and that numerous changes can be made without departing from thespirit and scope of the invention.

I claim:
 1. Method of preparing aldol condensation catalysts whichcomprises the steps of:(1) Adding mixed aqueous solutions of divalentand trivalent inorganic salts to a solution of a stoichiometric amountof sodium hydroxide and sodium carbonate at ambient temperature withvigorous stirring whereby a slurry is obtained; (2) Heating the slurryfrom (1) at about 60°-200° C. until crystallization occurs providing asynthetic anionic clay mineral having the generic formula:

    M.sub.m N.sub.n (OH).sub.(2m+2n) A.sub.a.bH.sub.2 O

whereinM is a divalent metal cation; N is a trivalent metal cation; A isa mono- , di- or trivalent anion which decomposes at about 300°-500° C.to form a volatile gas; m and n are such that m/n has values of 1 toabout 6; a is a number with the provisos that when A is a monovalentanion, a=n, when A is a divalent anion, a=1/2n, and when A is atrivalent anion a=1/3n, and b is an integer having values of 1 to 10;(3) Filtering the solids from the slurry in (2); (4) Washing thefiltered solids with water; (5) Heating the filtered solids from (4) toa temperature of about 300° to about 600° C.; and (6) Recovering theheated solids from (5) as an aldol condensation catalyst.
 2. Methodclaimed in claim 1 wherein the synthetic anionic clay mineral has theformula:

    M.sub.6 N.sub.2 (OH).sub.16 A.4H.sub.2 O.


3. Method claimed in claim 2 wherein M is Mg⁺² and A is CO₃ ⁻². 4.Method claimed in claim 2 wherein M is Ni⁺², N is Cr⁺³, and A is CO₃ ⁻².5. Method claimed in claim 2 wherein M is a mixture of Ni⁺² and Mg⁺², Nis Al⁺³ and A is CO₃ ⁻².
 6. Method claimed in claim 2 wherein M is Mg⁺²,N is a mixture of Al⁺³ and Cr⁺³ and A is CO₃ ⁻².
 7. Method claimed inclaim 2 wherein M is Zn⁺², N is Cr⁺³ and A is CO₃ ⁻².
 8. Mineral made bythe method claimed in claim
 3. 9. Mineral made by the method claimed inclaim
 4. 10. Mineral made by the method claimed in claim
 5. 11. Mineralmade by the method claimed in claim
 6. 12. Mineral made by the methodclaimed in claim
 7. 13. Method claimed in claim 1 wherein A is amonocarboxylate anion.
 14. Method claimed in claim 13 wherein themonocarboxylate anion is an acetate anion.
 15. Method claimed in claim 1wherein A is a nitrate anion.
 16. Method claimed in claim 1 wherein A isa polycarboxylate anion.
 17. Method claimed in claim 16 wherein thepolycarboxylate anion is an oxalate anion.